1525 / 2024-09-27 21:52:19
Pronounced NO, N2O and H2S dynamics in anoxic microenvironments of seagrass leaf epiphytic biofilms, with enhanced production under varying environmental conditions
seagrass,anaerobic microbial activity,microenvironment,deoxygenation,water eutrophication
Session 59 - Impacts of Climate and Biogeochemical Extremes on Marine Organisms and Ecosystems
Abstract Accepted
The seagrass phyllosphere can become anoxic in darkness owing to epiphyte respiration. Within anoxic microenvironments, anaerobic microbial processes can potentially produce phytotoxins and greenhouse gases, but the actual occurrence of such processes in seagrass epiphytic biofilms remains uncertain.
Here, we used microsensors to measure O2, NO, N2O and H2S concentration gradients, as well as NO and O2 dynamics within epiphytic biofilms on seagrass (Zostera marina) leaves under varying environmental conditions. We found pronounced production of NO, N2O and H2S in anoxic parts of the seagrass phyllosphere. Under hypoxic seawater conditions, the anoxic zone expanded within the seagrass leaf microenvironment, with NO and H2S reaching maximal concentrations of 1.0 and 4.4 μmol L-1, respectively. Furthermore, increasing seawater temperatures (from 14 to 24 °C) stimulateed H2S production and accumulation within anoxic seagrass phyllospheres. The denitrification process was enhanced in eutrophic seawater, where the highest N2O concentration in the epiphytic biofilms reached 5.9 μmol L-1. Part of the phytotoxic NO and H2S diffused into the seagrass leaves, while no NO escaped the biofilm. In contrast, N2O emission from the biofilm in hypoxic and eutrophic seawater reached 9.6 μmol N2O m-2 day-1. Such release of the potent greenhouse gas N2O from seagrass leaves with epiphytic biofilms could potentially offset the carbon burial capability of seagrass meadows.
Multiple environmental stress conditions involving high temperatures, eutrophication and reduced O2 availability in the water-column, can thus stimulate denitrification and sulfate reduction within anoxic leaf microenvironments, negatively impacting seagrass fitness and ecological function.
Here, we used microsensors to measure O2, NO, N2O and H2S concentration gradients, as well as NO and O2 dynamics within epiphytic biofilms on seagrass (Zostera marina) leaves under varying environmental conditions. We found pronounced production of NO, N2O and H2S in anoxic parts of the seagrass phyllosphere. Under hypoxic seawater conditions, the anoxic zone expanded within the seagrass leaf microenvironment, with NO and H2S reaching maximal concentrations of 1.0 and 4.4 μmol L-1, respectively. Furthermore, increasing seawater temperatures (from 14 to 24 °C) stimulateed H2S production and accumulation within anoxic seagrass phyllospheres. The denitrification process was enhanced in eutrophic seawater, where the highest N2O concentration in the epiphytic biofilms reached 5.9 μmol L-1. Part of the phytotoxic NO and H2S diffused into the seagrass leaves, while no NO escaped the biofilm. In contrast, N2O emission from the biofilm in hypoxic and eutrophic seawater reached 9.6 μmol N2O m-2 day-1. Such release of the potent greenhouse gas N2O from seagrass leaves with epiphytic biofilms could potentially offset the carbon burial capability of seagrass meadows.
Multiple environmental stress conditions involving high temperatures, eutrophication and reduced O2 availability in the water-column, can thus stimulate denitrification and sulfate reduction within anoxic leaf microenvironments, negatively impacting seagrass fitness and ecological function.